1. Field of the Invention
The present invention generally relates to a paper transmitting mechanism, and more particularly to a paper transmitting mechanism with a function of detecting position of the paper and adjusting the clamping force according to the position of the paper.
2. The Related Art
With reference to FIG. 1, a common document feeder comprises a transmitting path which is defined by plenty of guiding walls and/or guiding units for guiding paper; and plenty of transmitting roller sets placed along the transmitting path to transmit paper piece by piece through the transmitting path.
The transmitting roller sets include a driving roller and a driven roller; the driving roller is connected to a driving device which drives the driving roller. The driven roller is pivotably mounted around the driving roller, and provides paper a proper clamping force and friction for transmitting.
However, paper won't be transmitted smoothly if the clamping force and the friction between the driving roller and the driven roller are too big or too small. For example, if the clamping force and the friction are too small, the paper is apt to slip during the transmitting, and makes images misplaced.
In opposite, if the clamping force and the friction are too big, the paper might be pulled by the transmitting roller sets upstream and downstream, and shakes the paper and twists the image.
In view of these disadvantages above, the paper transmitting mechanism and the document feeder should be improved.